Polymers, such as polyethylene, have long been used as sachets (i e, small bags) for the packaging of products that have a short use cycle (e.g., less than about 12 months). Sachets are generally composed of multiple layers that include different types of materials to provide desired functionality, such as sealing, barrier, and printing. In food packaging, for example, a sachet is often used as a protective agent to package food, and is quickly disposed of after the contents are consumed. Sachets are also used to house a variety of consumer products that have a short use cycle, such as products for hair care, beauty care, oral care, health care, personal cleansing, and household cleansing. These sachets often enclose just enough product for a single use, and are often discarded as litter after that single use.
In developed parts of the world, the discarded sachets typically end up in a solid waste stream, which is incinerated or placed in landfills. In regions without modern solid waste infrastructure, used sachets are commonly discarded as litter on the soil and in surface waters. While some efforts at recycling the sachets have been made, the nature of the different polymers that compose the layers of the sachets, the presence of metals, the way the sachets are produced, and the way they are converted to products limit the number of possible recycling applications. For example, repeated processing of even pure polymers results in material degradation and, consequently, poor mechanical properties. In addition, the different grades of chemically similar plastics that are mixed during the recycling process can cause processing problems that make the reclaimed material inferior or unusable.
Some plastics manufacturers have introduced additives, such as oxo-biodegradable additives and organic materials, into traditional polymers (e.g., polyethylene, polypropylene, polystyrene, polyvinyl chloride) to promote biodegradation of the polymers in both aerobic environments (e.g., composting, soil) and anaerobic environments (e.g., landfills, sewage systems).
Oxo-biodegradable additives are often compounded into a polymer in a concentration of about 1 wt. % to about 5 wt. %, based on the total weight of the polymer, and consist of transition metals that theoretically foster oxidation and chain scission in plastics when exposed to heat, air, light, or a mixture thereof. The shortened polymer chains theoretically can be consumed by microorganisms found in the disposal environment and used as a food source. However, the fragmentation is not a sign of biodegradation, and there is no data to show how long these plastic fragments will persist in the soil or marine environments. Further, data have shown that moisture will retard the fragmentation process for months or longer. From a practical perspective, a plastic bag that is littered in the desert will probably fragment in a few months, but the fragments will persist for years or longer. If the same bag is littered in a cold, dark wet forest, it is unlikely that the bag will even fragment for months or years.
When organic materials, nonlimiting examples of which include, cellulose, starch, ethylene vinyl acetate, and polyvinyl alcohol, are used as additives in traditional plastics, some portion of the additive itself will biodegrade and generate carbon dioxide and methane. No data demonstrate that the remaining 95 wt. % to 99 wt. % of the traditional plastic will also biodegrade. The Biodegradable Products Institute (BPI) recommends that a supplier demonstrate that 90% of the entire plastic film or package, not just the additive, be converted to carbon dioxide under aerobic conditions, and carbon dioxide and methane under anaerobic conditions.
Sachets composed of biodegradable polymers seem to provide a solution to the problems described above, which are more efficacious or practical than recycling and/or the use of oxo-biodegradable and organic material additives. As used herein, the term “biodegradable polymers” are those that are capable of undergoing natural decomposition into carbon dioxide, methane, water, inorganic compounds, biomass, or a mixture thereof, in which the predominant mechanism is the enzymatic action of microorganisms that can be measured by standardized tests, in a specified time, reflecting relevant disposal conditions. In the presence of oxygen (aerobic biodegradation), these metabolic processes yield carbon dioxide, water, biomass, and minerals. Under anaerobic conditions (anaerobic biodegradation), methane may additionally be produced.
The attributes that render a polymer biodegradable, however, also may prevent it from being used for its intended purpose. Often, biodegradable polymers are moisture sensitive (i.e., can absorb significant amounts of water, swell, lose strength or thickness, or dissolve when exposed to aqueous media), thermally sensitive (i.e., have a melting point or glass transition temperature below about 65° C., or a Vicat softening point of less than about 45° C.), mechanically limited (i.e., a product formed from the polymer is too stiff, too soft, suffers from poor tensile strength or tear strength, or has insufficient elongation properties), and/or are difficult to process by conventional melt processes (e.g., cast film extrusion, blown film extrusion) into films. Properties such as tensile strength, tensile modulus, tear strength, and thermal softening point determine to a large extent how well a film will run on converting lines.
Biodegradable, metallized cellulose films (e.g., NatureFlex™ by Innovia LLC) have been used to form 12″×2″ sachets that are capable of containing dry products in dry environments. However, these sachets have limited success when filled with liquid consumer products. For example, when these sachets were filled with water and allowed to sit overnight, visible cracking of the metallized film was observed, and the sachets failed within 24 hours, as evidenced by droplets visibly seeping through the film.
Degradable sachets suitable for containing a single serving of dry products, such as sugar, are also known. These sachets are composed of paper that is extrusion coated with a grade of MATER-BI™ thermoplastic starch film manufactured by Novamont.
Films composed of a biodegradable polymer layer are described in U.S. Patent Application Publication No. 2009/0286090, incorporated herein by reference. However, these films require high barrier properties to achieve their desired performance characteristics. To realize these high barrier properties, it is necessary to incorporate non-degradable materials (e.g., polyvinylidene chloride; polyvinyl alcohol; polyvinyl acetate; polyolefins, such as polyethylene and polypropylene; polyamides; extrudable grade ethylene vinyl acetate; extrudable grade ethylene acrylic acid; ethylene vinyl alcohol copolymers (EVOHs) and combinations thereof, such as polyamide/EVOH/polyamide coextrusion) into the biodegradable polymer layer. Thus, these films are only partially biodegradable.
A fully degradable film that is a multilayer laminate is described in U.S. Patent Application Publication No. 2008/0038560, incorporated herein by reference. However, laminates are themselves undesirable because the lamination process is costly.
Japanese Patent Application 2005/111783, incorporated herein by reference, discloses packages with a resin composition of polylactic acid and lactic acid group co-polyesters upon which aluminum was vapor deposited. However, these films only degrade under industrial composting conditions and do not biodegrade in an open environment.
Polyhydroxyalkanoates (PHAs) also have been of general interest for use in forming biodegradable films. For example, U.S. Pat. No. 5,498,692, incorporated herein by reference, discloses a biodegradable film composed of a polyhydroxyalkanoate copolymer that has at least two randomly repeating monomer units. This film can be used to form, for example, grocery bags, food storage bags, sandwich bags, resealable Ziploc®-type bags, and garbage bags. PHA films or other biodegradable films may also be used to create a sachet, although a sachet comprising only PHA will not meet the barrier requirements for most consumer goods.
Although PHAs are biodegradable, their actual use as a plastic material has been hampered by their thermal instability. PHAs tend to have low melt strengths and may also suffer from a long set time, such that they tend to be difficult to melt process. Further, PHAs tend to undergo thermal degradation at very high temperatures (i.e., the temperatures that can be encountered during melt processing). Further still, PHAs have poor gas and moisture barrier properties, and are not well suited for use as packaging materials, as described in U.S. Patent Application Publication No. 2009/0286090, incorporated herein by reference.
None of the single use sachets that are currently in use and composed of a single layer of biodegradable polymers (i.e., no laminate) that can withstand the manufacturing process, have a long shelf life, meet barrier requirements, and biodegrade within a relatively short time period in an open environment.